Intensity control



July 5, 1932. F. SCHROTER ET AL INTENSITY CONTROL Filed Aprii 5, 1930 INVENTORS FRITZ SCHROTER BY woLy eglisoEnmAnn ATTOlNEY Patented July 5, 1932 I 1 UNITEDSTATES Fm'rz scHRo'r nAND WOLFGANG FETDEBM'ANN, or BERLIN, GERMANY, assrenons i 5' particularly T granted 'on ,Bronk and Hans Rukop,

PATENT OFFICE l TO TELEFUNKEN GESELLSCHAFT FUR DRAHTLOSE TELEGRAPI-IIE M. B. 11., OF IBER- LIN, GERMANY, A CORPORATION 0F GERMANY INTENSITY CONTROL Application med n rnaisso, Serial No.

I The present invention relates to aymethod and means of accomplishing theautomatic regulation of the incoming intensity of signal strength of received signal energy, and is adapted to short-wave picture In U. S. Patent #1,82(),335, August 25,1931,to Otto Von a system of a related type is disclosed, wherein the amplifica telegraphy.

tion of the incoming picture impulses or signals from one line of the picture to the next is made a function of .the variations or changes in signal strength in so far as part of the scanned surface, for instance, the zone where the outgoing picture holdingstrip is secured, ismade to serve for the transmission .1?) indicates the same impulse of a regulating energy,thedegree of amplification in thecourse of the following or succeeding drum revolution being made a function of and dependent. upon the strength or intensity with which said regulating energy is received. i

The aim and purpose ofthe present invention resides in the combination of the means disclosed in the above referred to application for the elimination of impulse spreading and the undesirable effects due thereto in highspeed picture or facsimile transmission, and a limiting system for further controlling the signal. a By the accompanying drawing the invention hasbeen illustrated in one of its preferred forms, by way ofexample, altho many modifications may suggest themselves to those skilled in the art towhich the invention is directed. In the drawing, Figla'discloses an impulse sent out from a transmitter; Fig. as received; Fig. 2 represents a conventional form of transmitter; and Fig. 3 represents areceiver for receiving signals transmitted from'a systemof the type shown by Fig. 2, forexample. Now making reference to the drawing, one peculiarity of short waves'quite recently discovered consists in that a short impulse a, as shown, for example, by Fig. 1a, sent out from the transmitter reaches the receiver apparatus in the shape of a more or less irregular signal, say, ofashapeasindicated at b in Fig. 16. It is supposed that the impulse a 'ment as shown by 441,972, and in Germany April 24, 1929.

In order to avoid this effect which is great-. I

1y undesirable in the case of high-speed facsimile transmission, the present invention has recourse to theobservation that the amplitudes of the impulses picked up at the receiving end and which flow more or less together, as shown by way of example by the curve 6 of Fig. 1b, are as a rule distinctly pulse presents the greatest amplitude or intensity, while the crests of the others are lower. This conditionmay change in that the second, third, fourthcrests of curve b may .assume the maximum amplitude. But such changes occur at a slow rate, indeed, when using the present invention, they neither impair the total impression or result of the facsimile document, nor the legibility of the same. The invention in more detail consists of the following:

The amplification in the receiver apparatus by the aid of the grid biasing potential of one of the tubes, most preferably in the first radio frequency stage,is so regulated that only those portions of the expanded or slightly shifted incoming signal will be recorded by the recorder means as exceed a certain liminal or threshold val-ueE For this purpose there is used, for instance, an arrange- Fig. 2 designates the transmitter, and in which Fig. 3 designates the receiver'apparatus. v

The transmitter of Fig. 2 does not distinguish itself from the equipment'customary in facsimile transmission work. The rays of .a luminoussource 1 are interrupted by a rapidlyrotating perforated light chopping disk 2 at a high rate of frequency. Bymeans of a lens 3 the picture or image of the source 1 is Figs. 2 and 3, in which unequal. In the case here shown, the first improjected in the shape of a scanning spot upon a record surface for transmission carried by the drum a while the diffuse rays reflected therefrom are made to impinge and act upon the annular photo-electric cell 5. 6 denotes the amplifier to which the picture current from the cell 5 is fed, and 7 represents the short-wave or even wire line transmitter modulated by the picture current. The outfit is so operated that, while the strip securing the picture and which occupies the angle on is passing, the transmission current is modulated with its maximum value under the light spot or that it is completely modulated at a certa-in value at the frequency governed by the perforated disk 2. This means that during this time interval the radiated energy has a certain and constant amplitude, and this is utilized for the regulation of the amplification at the receiving end in accordance with the disclosure of the above named copending application.

Referring now to the receiver apparatus shown by Fig. 3, 8 denotes the tuned circuit which is associated with the antenna or a system of directional antennae. Numeral 9 represents a radio frequency amplifier tube and 10 a choke-coil. Further amplification is effected by stages 11 (such as an intermediatefrequency amplifier) and 12 (an audio frequency amplifier). The current furnished from stage 12 is alternately fed by way of a contact slide 13 and a rotating distributer to segments 14 and 18. By way of segment 14, the current flows to light relay or valve 15 whose luminous spot, subject to the control of the incoming current, is projected through lens 16 upon the recorded drum 17.

While the transmitter drum 4 occupies a position as shown in the drawing where no part of the picture is sent out, the distributer revolving (like the drum 17) in synchronism and under co-phasal condition with the sending end, is in touch and contact with the segment 18. It is preferable to make the latter somewhat shorter than would correspond to the angle or, so that, quite independently of slight phase errors and discrepancies in the rotation in the receiver apparatus compared with that in the transmitter, the regulating amplitude will. be able to act during an invariable length of time. i

From the segment 18 the incoming current flows back through the resistance 19 to the audio frequency amplifier 12. The fall of otential occasioned across resistance 19 governs tube 20 operated to act as a rectifier and the plate current thereof will charge the large condenser 21 to a more or less high value according to the strength of the incoming signals. In order that this value may be correctly determined for each line of the picture, the condenser 21 must be discharged either completely or else to a certain residual or initial potential briefly before each new charge. The contacts 24, 25 serve for this purpose, since they can be moved in relation to each other, and may be closed for a short length of time by the cam or tappet of disk 26 during the rotation thereof. The disk 26 revolves in synchronism with the distributer 18, 14, 18 and the picture drum 17, and its phase in relation to said parts is such that the condenser 21 will be discharged in a way as stated briefly before the distributer wiper 13 has reached the segment 18. The charge of condenser 21 produces a fall of D. C. potential across a high resistance 27 connected in the grid circuit of tube 9 whereby the amplification thereof is regulated in that the Working point on the characteristic of tube 9 is shifted in accordance with the invention. The choke-coils 22, 23, serve the purpose of blocking the grid circuit 8 against radio frequencies. The resistance 27 must be so high that the potential of the condenser 21 during a picture line will not appreciably drop, and the same may be bridged (shunted) for radio frequency by means of a small capacity. Resistance 27 moreover may be inserted in the plate circuit of an input tube presenting a high reciprocal amplification factor and the grid of which is controlled by the charge of capacity 21. If this tube operates without grid current, then the fall of potential across resistance 27 will remain constant until a new adjustment is effected.

The stronger the regulating energies or amplitudes received in the course of the regulating period due to segment 18, the more marked will be, in the arrangement here described,the negative biasing potential of the grid of tube 9. Hence, when operating upon the lower end of its plate characteristic, then the slope of the curve portion used for the amplification during the following picture period will have different values, according to the signal strength, and thus the energy produced by amplifier 12 can be regulated in well-known manner. Hence, there are ways and means to adjust the signal potential acting upon the light valve 15 independently of the strength of the incoming picture signals in such a way that Fig. 16, only that part will be recorded which exceeds the suitably chosen liminal value E the latter being determined by adjusting the sensitiveness of the light relay itself or else by grid blocking of a tube connected below the light relay. 7 i

It will be understood that for amplification regulation in the sense as hereinbefore outlined other circuit schemes may be resorted to without departing from the scope and spirit of the invention.

Having now described our invention, what we claim and desire to secure by Letters Patent is the following:

' 1. An apparatus for eliminating intensity fluctuations in receiving systems comprising of the curve 6, shown by plifying means,

means for receiving signals, means for recording messages in accordance with said received signals, and capacity means for automatically controlling the sensitivity of said signal recording means in accordance with the strength of signals received during predetermined periods of time separating successive recording actions.

2. An apparatus for eliminating intensity fluctuations in radio reception systems com-e prising means for receiving signals, means for converting received signals into light impulses of intensities proportionate to the received signals, and capacity means for periodically controlling the received signal energy in accordance with the intensity thereof as received over time periods substantially less than the time period for which the con-- trol is to be effective.

3. An apparatus for eliminating intensity fluctuations in radio reception systems comprising means for receiving signals, means for amplifying said received signals, means for converting said amplified signals into a visible record of the received signals, and capacity means for controlling the amplification during predetermined periods of time in accordance with the strength of received signals during a relatively small portion of said predetermined time.

4. An apparatus for eliminating intensity fluctuations in radio reception systems comprising means for receiving signals, means for amplifying said received signals, means for converting said amplified signals into a record of the received signals, capacity means for controlling the amplification during predetermined periods of time in accordance with the strength of signals received during a relatively small portion of said predetermined time, and means for restoring the entire system to an uncontrolled degree of amplification during .a minute time period prior to the period of control, j a

5. An apparatus for eliminating intensity fluctuations in radio receiving systems comprising signal receiving means, signal amsignal translating means, and capacity means for controlling the amplification of said received signals during predetermined periods of time 1n accordance with the strength of the received signals during a relatively small portion ofsaid' predetermined time. d

6. In a system for eliminating intensity fluctuations in radio reception systems, means for receiving, amplifying and translating determined portion of said time period whereby the charge acquired by said element is adapted to leak therefrom during the absence of said charging influence so as to control the amplification of said received signals, and means for discharging said capacity element during an infinitesimal time period immediately prior to the time of charging thereof. v

7.. An apparatus for eliminating intensity fluctuations in radio reception systems comprising means for receiving, amplifying and converting signals into a message record, capacity-means for controlling the amplification during predetermined periods of time in accordance with the strength of signals received during a relatively small portion of said predetermined time, and means operating at a rate proportionate to the rate at which a predetermined series of signals are received for restoring the entire system to an uncontrolled degree of amplification during a minute time period prior to the period of control.

8. An apparatus for eliminating intensity fluctuations in radio receiving systems comprising signal receiving means, signal amplifying means, signal translating means, capacity means for controlling the amplification of said received signals during predetermined periods of time in accordance with the strength of the received signals during a relatively small portion of said predetermined time, and means for restoring the entire system to a substantially uncontrolled stateat a time period immediately prior to the period of time over which said controlling action is effective. a

9. In a system for eliminating intensity fluctuations in radio reception systems, means for receiving, amplifying and recording signals, a capacity element for controlling the degree of amplification of said signals for a predetermined time period, means for charging said capacity element during a predetermined portion of said time period whereby the charge acquired by said element is adapted to leak therefrom during the absence of 

